Fungal infection

Question 1

Differences between fungi and bacteria other than just differences between eukaryotes and prokaryotes

Answer 1

Fungi = eukaryotic
Bacteria = prokaryotic
- Fungi are dimorphic hyphae or yeasts
- Fungi lack chloroplasts
- Fungi have membrane-bound organelles
- Fungi cell membranes contain ergosterol not cholesterol
- Fungi divide by budding, not binary fission
- Fungal cell walls contain glucans and chitins instead of peptidoglycan

Question 2

The three types of illnesses caused by fungi

Answer 2

Allergies
Mycotoxicoses
Mycoses

Question 3

Cause of allergies and types of allergies

Answer 3

• Fungal spores in the air upon inhalation or contact with the skin
• Rhinitis (inflammation of nasal mucosa)
• Dermatitis
• Asthma
• ABPA (allergic bronchopulmonary aspergillosis)

Question 4

Symptoms of allergies

Answer 4

• Congestion
• Sneezing
• Itching
• Watery eyes
• Coughing
• Headache

Question 5

Definition of mycotoxicosis

Answer 5

Toxic reaction caused by inhalation or ingestion of secondary metabolites of moulds that cause a negative effect on humans

Question 6

Example of a myotoxicosis

Answer 6

Aflatoxin produced by aspergillum flavus

- Presence of aflatoxin and hepatitis B = increased risk of liver cancer

Question 7

Symptoms of mycotoxicoses

Answer 7

• Breathing problems
• Dizziness
• Severe vomiting
• Diarrhoea
• Dehydration
• Hepatic failure then renal failure 6 days later

Question 8

How are mycoses classified and what are the four classifications?

Answer 8

Classified by level of tissue affected

• Superficial
• Cutaneous
• Subcutaneous
• Systemic (deep)

Question 9

Features of superficial mycoses

Answer 9

• Present on surface of skin
• Infection of skin or hair shaft
• No living tissue invaded
• No cellular response from host

Question 10

Examples of superficial mycoses

Answer 10

Piedraia hortae
Trichosporon beigelli
Malassazia globosa
Phaeoannellomyces wenecki

Question 11

Features of cutaneous mycoses

Answer 11

• Confined to epidermis
• Dermatophytes or keratinophilic fungi
• Produce extracellular enzymes that hydrolyse keratin (keratinases)
• Inflammation caused by host response to metabolic by-products

Question 12

Examples of cutaneous mycoses

Answer 12

Epidermophyton
Trychopyton
Microsporum
Candida albicans

Question 13

Definition of subcutaneous mycoses

Answer 13

Chronic, localised infections of the skin and subcutaneous tissue following traumatic implantation of the infective agent

Question 14

Examples of subcutaneous mycoses

Answer 14

Sporotrichosis (sporothrix)
Chromoblastomycosis (several spp.)
Mycetoma (several spp.)

Question 15

Mechanisms of action of anti fungal drugs targeting fungal cell membrane

Answer 15

• Inhibition of ergosterol synthesis by inhibiting fungal cytochrome p450 enzymes
• Polyene antifungals form pores in the membrane by binding to ergosterol and promoting leakiness
• Azole antifungals inhibit 14alpha-demethylase which produces ergosterol

Question 16

Mechanisms of action of anti-fungal drugs targeting DNA synthesis

Answer 16

• Some compounds selectively activated by fungi, arresting DNA synthesis
• Pyrimidine analogues (molecules similar to pyrimidine bases) can target fungi-specific DNA synthesis pathways with not worry of host cells’ DNA synthesis being impaired

Question 17

Mechanisms of action of antifungals targeting fungi cell walls

Answer 17

• Inhibition of beta 1,3 gluten synthase

- Prevents synthesis of glucan which makes up fungal cell wall with chitin

Question 18

Superficial mycoses definition

Answer 18

Fungal infections limited to the outermost layers of the skin and hair

Question 19

Systemic mycoses definition

Answer 19

Fungal infections infecting internal organs either by primary or opportunistic pathogens

Question 20

Primary pathogen definition

Answer 20

Pathogen able to establish infection in a healthy host

Question 21

Opportunistic pathogen definition

Answer 21

Pathogen requires compromised host to establish infection

Question 22

Example of superficial mycoses and its features

Answer 22

Superficial candida infections

• Usually due to impaired epithelial barrier functions
• Occur in all age groups
• Most common in newborn and elderly

Question 23

Examples of systemic mycoses and their features

Answer 23

Systemic candida infections
- Opportunistic
- Chemotherapy, gut-related surgery, catheters all increase risk of infection
Systemic invasive pulmonary aspergillosis
- Incidence caused by underlying condition
- Organ or stem cell transplant 15%
- Myeloid and lymphatic leukaemia 10%
- AIDS 3%